TM 55-1510-222-10CHAPTER 3AVIONICSSection I. GENERAL3-1.INTRODUCTION.Except for mission avionics, this chapter coversall avionics equipment installed in the RC-12K aircraft.It provides a brief description of the equipment, thetechnical characteristics and locations. It coverssystems, controls, and provides the proper techniquesand procedures to be employed when operating theequipment. For more detailed operational informationconsult the vendor manuals that accompany the aircraftloose tools.3-2.AVIONICS EQUIPMENT CONFIGURATION.The aircraft avionics covered, consists of threegroups of electronic equipment. The communicationgroup consists of the interphone, UHF command, BUVOW, VHF FM, VHF command and HF commandsystems. The navigation group provides the pilot andcopilot with the instrumentation required to establish andmaintain an accurate flight course and position, and tomake an approach on instruments under InstrumentMeteorological Conditions (IMC). The navigation groupincludes equipment for determining altitude, attitude,position, destination, range and bearing, headingreference, groundspeed, and drift angle. Thetransponder and radar group includes an identification,position, emergency tracking system, a radar system tolocate potentially dangerous weather areas, and a radarsystem to differentiate between friendly and unfriendlysearch radar.NOTEAll avionics equipment require a 3-minute warmup period. The weatherradar has an automatic time delay of 3to 4 minutes.3-3.POWER SOURCE.a.DC Power.DC power for the avionicsequipment is provided by four sources: the aircraftbattery, left and right generators, and external power.Power is routed through two 50-ampere circuit breakersto the avionics power relay which is controlled by theAVIONICS MASTER POWER switch in the overheadcontrol panel (fig. 2-13). Individual system circuitbreakers and the associated avionics busses are shownin figure 2-6. With the switch in the ON (forward)position, the avionics power relay is de-energized andpower is applied through both the AVIONICS MASTERPOWER No. 1 and No. 2 circuit breakers to theindividual avionics circuit breakers in the overheadcircuit breaker panel (fig. 2-6). In the OFF (aft)position, the relay is energized and power is removedfrom the avionics equipment.NOTEIf the AVIONICS MASTER POWERswitch fails to operate, power to theindividual avionics circuit breakerscan be provided by pulling the 5-ampere circuit breaker, placardedAVIONICS MASTER CONTR, locatedin the overhead circuit breaker panel(fig. 2-6).When external power is applied to the aircraft, theavionics power relay is normally energized, removingpower from the avionics equipment. To apply externalpower to the avionics equipment, move the AVIONICSMASTER POWER switch to the EXT PWR position.This will de-energize the avionics power relay and allowpower to be applied to the avionics equipment.b.Single-Phase AC Power.AC power for theavionics equipment is provided by two inverters. Theinverters supply 115-volt and 26-volt singlephase ACpower when operated by the INVERTER No. 1 or No. 2switches (fig. 2-13). Either inverter is capable ofpowering all avionics equipment requiring AC power.AC power from the inverters is routed through fuseslocated in the nose avionics compartment.c.Three-Phase AC Power.Three phase ACelectrical power for operation of the inertial navigationsystem and mission avionics is supplied by two DCpowered, 3000 volt-ampere, solid state, three phaseinverters. The three phase inverters are controlled bytwo three-position switches located in the missioncontrol panel (fig. 4-1) placarded No. 1 INV OFF ONRESET and No. 2 INV OFF ON RESET.3-1